1. Field of the Invention
This invention relates to apparatus for controlled metering of particulate material, and more particularly to apparatus capable of controlled metering of agricultural products.
2. Description of the Prior Art
It is desirable in many applications to meter a flow of particulate material such as various agricultural products with a controlled, uniform thickness. For this purpose a form of gate has frequently been used which consists of a metal plate or block positioned at a desired height above a conveyor belt along which the material is moved. The thickness of the material permitted to pass under the gate is limited by the clearance between the plate and the conveyor belt, the remaining material being held back by the gate.
One problem frequently encountered with this type of metering arrangement is that light fluffy materials such as flour, many fertilizers, powdered lime and certain seeds have a tendency to back up at the gate and interfere with the even metering of material. The material typically begins to bridge or back up above the gate, with the bridging effect gradually expanding in a downward direction. The result is an uneven metering of material at an average thickness less than the amount desired, and if left undisturbed in some cases can eventually cut off the flow of material altogether.
One prior art device which attempts to alleviate some of these problems is disclosed in U.S. Pat. No. 3,154,117 to Florin. In this patent an endless belt is supported by a framework above a horizontal conveyor belt. An adjustable pivot mount is provided to enable the endless belt to be moved to and from the conveyor belt. Turning of the endless belt is said to aid in forcing material out along the conveyor belt to a downstream filling compartment, and at the same time limits the amount of material that will feed out along the conveyor belt at any given instant. Near the end of the conveyor belt a series of raking fingers are secured to a rotatable shaft. The shaft is rotated, apparently in a direction such that the movement of the raking fingers adjacent the conveyor belt is opposite to the direction of the conveyor belt movement. The fingers pick material off of the conveyor belt as it approaches the filling compartment, thereby preventing large quantities of the material from being suddenly dropped into the compartment.
While the Florin patent may address some of the problems outlined above, the endless belt and rake mechanism proposed are quite bulky, and would appear to add considerably to the size, complexity and cost of the metering apparatus.
Another desirable characteristic in a metering device for certain applications is the ability to accomplish "singulated" metering, ie., metering of one particle at a time in a single line. This ability is important, for example, in feeding certain seeds for planting. In addition to the possible problems of backups caused by an overhead gate, it is also important that the device meter in a fashion that produces only a single line of separated particles. Several methods have been used in the prior art to accomplish a singulated feed. In one approach seeds are carried inside a perforated rotating drum. Air pressure keeps the seeds inside the drum until the drum is rotated to a position at which the air pressure is cut off, permitting seeds to fall into a trough for metering. Another method uses a small cup about the size of a seed to capture one seed at a time from a pile, while in a third method, used mostly for laboratory work, seeds are captured one-at-a-time by a vaccum syringe.
An example of a device for singulated metering is disclosed in U.S. Pat. No. 4,105,398 to Disch et al. This device is designed to permit random loading of work pieces for passage through a furnace. An aligning means is provided in the form of a funnel, one side wall of which is movable to align the randomly positioned work pieces in single file. The position of the other sidewall forming the funnel is fixed. While this arrangement is disclosed as being applicable to the loading of metal workpieces for passage through a furnace, it might be applicable to the movement of particulate material in general. However, the workpieces illustrated in the patent are quite large and all lie directly on the conveyor, rather than being piled on top of each other. Accordingly, no provision is made for controlling the height of workpieces transported by the system, such as the gate mechanisms referred to above.